Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $127.39   11.276%   $141.7545   $141.75   $141.75   $141.80  
  Purchase #2 $214.99   10.401%   $237.3511   $237.35   $237.35   $237.40  
  Purchase #3 $73.57   3.629%   $76.2399   $76.24   $76.25   $76.20  
  Purchase #4 $129.59   8.253%   $140.2851   $140.29   $140.30   $140.30  
  Purchase #5 $45.93   8.144%   $49.6705   $49.67   $49.65   $49.70  
  Purchase #6 $172.56   3.241%   $178.1527   $178.15   $178.15   $178.20  
  Purchase #7 $172.26   8.392%   $186.7161   $186.72   $186.70   $186.70  
  7 purchase totals = $936.29       $1,010.1699   $1,010.17   $1,010.15   $1,010.30